Studies are underway with regard to atherosclerosis at the clinical levels, in experimental animals and in vitro. Studies include development of noninvasive techniques for the diagnosis of atherosclerosis in vivo, emphasizing changes in myocardial perfusion and using scanning techniques after injection of radioisotopes to label myocardium. Intensive studies of lipoprotein biosynthesis in cultured liver cells and degradation of lipoproteins by cultured cells (adipocytes, myocardial cells, aortic smooth muscle cells and hepatocytes) are underway. The enzymes degrading lipoproteins are being purified and characterized. Lipoprotein lipase from adipose tissue has been purified and its properties are under further investigation. The lipase released from the liver after heparin injection has also been purified. Studies will be done to explore the effects of combined degradation of lipoproteins by these two distinct enzymes. The post-heparin phospholipase activity in plasma is under study with regard to its effects on lipoproteins and again the interactions of it and other enzymes degrading lipoproteins.